1. Technical Field of the Invention
This invention relates generally to communication systems and, more particularly, to radio receivers and transmitters used within such communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire-lined communications between wireless and/or wire-lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera, communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or multiple channels (e.g., one or more of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel or channels. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel, or channels. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio-transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver,(e.g., a station for in-home and/or in-building wireless communication networks, RE modem, etc.). As is known, the receiver receives RF signals, demodulates the RF carrier frequency from the RF signals via one or more intermediate frequency stages to produce baseband signals, and demodulates the baseband signals in accordance with a particular wireless communication standard to recapture the transmitted data. The transmitter converts data into RF signals by modulating the data in accordance with the particular wireless communication standard to produce baseband signals and mixes the baseband signals with an RF carrier in one or more intermediate frequency stages to produce RF signals.
To recapture data from RF signals, a receiver includes a low noise amplifier, down conversion module and demodulation module. To convert data into RF signals, a transmitter includes a power amplifier, an up-conversion module and a modulation module. For radio frequency integrated circuits (RFICs), it is desirable to provide the low noise amplifier and the power amplifier with differential RF signals, instead of single-ended RF signals, to improve noise performance and common mode rejection. To convert received single-ended RF signals into differential RF signals for a receiver, and to convert differential RF signals into single-ended signals for a transmitter, the receiver and/or the transmitter includes a balun (i.e., a balanced/unbalanced transformer).
Until very recently, the baluns were off-chip, i.e., on the printed circuit board, and were typically implemented in the form of micro-strip lines. However, for semiconductor chip designs, it is desirable to place RFIC baluns on-chip to reduce the cost of off-chip printed circuit board components. Recent attempts to integrate a balun onto a radio frequency integrated circuit have had limited success. For example, parallel winding, inter-wound winding, overlay winding, single planar, square wave winding, and concentrical spiral winding on-chip baluns have been tried with limited success. Each of these on-chip baluns suffers from one or more of low quality factor, (which causes the balun to have a relatively large noise figure and large energy loss); too low of a coupling coefficient (which results in the inductance value of the balun not significantly dominating the parasitic capacitance making impedance matching more complex); asymmetrical geometry (which results in degradation of differential signals); and a relatively high impedance ground connection at the operating frequency.
Other problems exist for RFICs that include on-chip baluns. For example, a power amplifier (PA) and a low noise amplifier (LNA) have different balun requirements. An LNA balun should provide a high voltage gain with a low noise figure (NF), which is directly related to the quality factor (Q) of the balun. An LNA balun should also be inductive enough such that only on-chip capacitors are needed for impedance matching with the antenna and to provide the required voltage gain. A PA balun, however, is required to support large currents, which requires a large track width of the transformer windings. The PA balun quality factor (Q) should also be high to provide high efficiency and high PA linearity and should have enough current amplification to provide a large current swing at the antenna output. The PA balun should also be inductive enough such that only on-chip capacitors are needed for impedance matching with the antenna.
Therefore, a need exists for an integrated radio frequency (RF) integrated circuit that includes a symmetrical balun antenna coupling structure that meets the differing operational requirements of both the LNA and the PA.